The present invention relates to an image forming method comprising a developing process by which an electrostatic latent image formed on a photoreceptor is developed by developer.
In an image forming method by an electrophotographic method, an electrostatic latent image formed on a photoreceptor is developed by developer containing toner for forming a toner image, and after the toner image is transferred onto an image supporting body such as a transfer sheet, or the like, an image is formed by being thermally fixed. On the other hand, the photoreceptor is discharged after a transfer process, next, any remaining toner on the photoreceptor is cleaned off, and the photoreceptor is ready for the next image formation.
In the fixing process in this type of image formation method, it is widely conducted to form a fixed image by a heat roller fixing unit. However, in fixing using the heat roller, fused toner components are transferred and adhered to the heat roller surface, and a so-called offset phenomenon, in which the adhered toner components transfer again onto the next feeding transfer sheet and stain the image, tends to occur. Conventionally, as a means for preventing the occurrence of the offset phenomenon, a releasing agent is contained in toner as a toner component so that the toner itself has the parting property. Here, low molecular weight polyolefine is appropriately used as the releasing agent.
Conventionally, as a photoreceptor used for image formation, inorganic photoreceptors such as selenium, cadmium sulfide, or the like, are widely known. Recently, however, from the viewpoint of the environmental contamination prevention, organic photoreceptors are more commonly being used. As such organic photoreceptors, a so-called multi-layered type organic photoreceptor is used in which a charge generation layer and a charge transport layer are stratified, through an adhesion layer when necessary, on a conductive supporting member.
However, when image formation is carried out using the above-described multi-layered type organic photoreceptor for a long period of time, since, normally, the charge transport layer made of resins containing charge transport materials is worn out by conducting the cleaning process or the like, image formation can not be effectively carried out for a long period of time.
In order to solve this problem, the following photoreceptors are disclosed:
an organic photoreceptor having, at the surface, a coating layer, in which hydrophobic silica is dispersed, is formed (Japanese Patent Publication Open to Public Inspection No. 118667/1990); PA1 an organic photoreceptor having, at the surface, a protective layer containing fine metallic particles or fine metallic oxide particles, having an average particle size of less than 0.3 .mu.m, is formed (Japanese Patent Publication Open to Public Inspection No. 30846/1982); and PA1 a photoreceptor having, at the surface, a protective layer, containing an inorganic filler, is formed (Japanese Patent Publication Open to Public Inspection No. 205172/1989).
These technologies are intended to increase the wear resistance of the photoreceptor surface, and thereby the durability of the photoreceptor, by providing the protective layer, containing each kind of fine particles, at the photoreceptor surface.
Due to the above technologies, although the wear resistance of the photoreceptor surface is increased, the hardness of the surface is also increased and thereby toner components tend to adhere to the photoreceptor surface. As a result, the following problem occurs: an insulating film is formed on the photoreceptor surface (so-called filming phenomenon), and thereby the potential voltage of the photoreceptor surface is not sufficiently lowered, resulting in fogging. Further, black-spot image defects occur on the formed image due to the influence of adhered toner components on the photoreceptor surface.
As described above, a stable image can not be formed for a long period of time, due to adopting such image forming methods, using photoreceptors which are intended to increase the durability by providing wear resistance on the photoreceptor with a surface protective layer.